1. Field of the Invention
The present invention relates to an oil seal means in a rotary piston engine and, more particularly, an oil seal means provided in a slide wall portion of a rotor of the engine for maintianing the air/oil tightness in the contact of the rotor side wall with the side housing.
2. Description of the Prior Art
The Wankel type rotary piston engine has a general structure such as shown in FIG. 1 wherein it comprises a casing composed of a rotary housing 1 having a trochoidal inner peripheral surface and side housings 2 which close the opposite open ends of said rotor housing, and a polygonal rotor 4 mounted in said casing to eccentrically rotate around an eccentric shaft 3 with apex portions thereof sliding over said trochoidal inner peripheral surface of said rotor housing. The rotor comprises an annular oil seal means generally designated by reference numeral 6 in each side wall 5 thereof for maintaining the air/oil tightness in the contact of said side wall of the rotor with the inner wall surface of the side housing.
One of the most basic sectional structures of such an oil seal means is shown in FIG. 2 which corresponds to the section along line II--II in FIG. 1. As shown in FIG. 2, the oil seal means comprises first and second annular oil seal grooves 7,7' concentrically formed in the side wall 5 of the rotor, and first and second combinations of oil seal rings 8,8', annular spring means such as annular corrugated springs 9,9' and annular elastic seal elements such as O-rings 10,10', said first and second combinations being mounted in said first and second grooves, respectively. The assemblies of said first and second grooves and said first and second combinations provide respectively first and second oil means arranged to be concentric to each other with an annular land 11 interposed therebetween.
When the rotor 4 incorporating these oil seal means eccentrically rotates around the eccentric shaft 3, the oil seal rings 8,8' are exerted not only a force which rotationally drives said rings along said annular grooves in the direction opposite the rotational direction of the rotor but also a force which drives the rings in radial directions of the rotor due to the reaction of the engaging side housing. Therefore, at a certain phase of rotation of the rotor, a particular portion of the rotor moves radially downward as shown by the arrow in FIG. 3 relative to the side housing, whereby the oil seal rings 8,8' are driven and biased upward in the figure. In this condition the concerned portion of the oil seal ring 8 is directly supported by the outer side wall of the annular oil seal groove 7 by way of an oil while the concerned portion of the oil seal ring 8' is supported by an annular land 11 by way of the annular elastic seal element 10' which is, therefore, prone to be compressed excessively. This means, as a matter of course, that in a diametrically opposite sectional portion the oil seal ring 8 is supported by the annular land 11 by way of the annular elastic seal element 10, which is then prone to be compressed excessively. When such an excessive compression of the annular seal element is repeated, the element fatigues, deteriorates and loses the elasticity thereby damaging the sealing performance of the oil seal means, resulting in an increase of the oil comsumption of the engine.